[PATCH] [LAA] Try to prove non-wrapping of pointers if SCEV cannot

[Adam Nemet]

Hi aschwaighofer, nadav, atrick, sanjoy,

Scalar evolution does not propagate the non-wrapping flags to values
that are derived from a non-wrapping induction variable because
the non-wrapping property could be flow-sensitive.

This change is a first attempt to establish the non-wrapping property in
some simple cases.  The main idea is to look through the operations
defining the pointer.  As long as we arrive to a non-wrapping AddRec via
a small chain of non-wrapping instruction, the pointer should not wrap
either.

I believe that this essentially is what Andy described in
http://article.gmane.org/gmane.comp.compilers.llvm.cvs/220731 as the way
forward.

http://reviews.llvm.org/D10472

Files:
  lib/Analysis/LoopAccessAnalysis.cpp
  test/Analysis/LoopAccessAnalysis/non-wrapping-pointer.ll

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